Astronomers, professionals and amateurs alike are gearing up for a rare celestial event in which planet Venus will cross the sun's disc on June 8.

The Venus transit is like a solar eclipse, except that in this case the planet being further away from the Earth than the Moon will be seen as a small dark dot moving across the solar disc.

In the run-up to the event, which last occurred in 1882, the Confederation of Indian Amateur Astronomers (CIAA) will launch a series of experiments all over the country, which also involves school students studying the event in detail, says general secretary Manoj Pai.

CIAA, which recently completed 10 years of its existence, represents astronomers and astronomy associations across the country.

It will carry out the experiments in collaboration with Science Popularisation Association of Communicators and Educators (SPACE) and Tamil Nadu Science Technology Centres. It will also conduct workshops and produce guidance material to educate students about the project.

The experiments to be carried out in three stages will kick off in February with nearly 1,000 students from schools all over the country making observations of the Sun to calculate the Earth's radius.

In the second stage of the experiment, astronomers and students will measure the position of Venus in the sky over 45 days. The data will be used to determine the angular separation between Venus and the Sun.

The third stage of the experiment involves actual observation of the transit. Astronomers using telescopes will determine the path the planet takes across the solar disc.

Data from the three experiments will be used to calculate the Astronomical Unit - the distance between the Earth and the Sun, says CIAA member Chander Devgun, who is actively involved with the project.

"One of the fundamental aims of astrophysics over the last 500 years has been the measurement of distance. Such a measurement in 1639 represented the beginning of astrophysics in England," he says.

Students from schools in Delhi, Baroda, Hyderabad, Minicoy Island (off the south Kerala coast) and other places have been roped in to carry out the observations.

Besides amateurs, professional astronomers are also gearing up for this mega-event. Observatories across the country, including the solar observatory in Udaipur, will track the transit using state-of-the-art technology.

Planetary transits have wowed star gazers for a long time, with astronomers launching expeditions to observe the great gigs in the sky. The 1761 and 1769 expeditions to observe the transits of Venus gave astronomers their first good estimate of the distance of the Sun from Earth.